The present disclosure relates to an adsorption based gas separation apparatus that separates oxygen from ambient air with beneficial improvements over the prior art in size, weight and energy consumed per unit of oxygen separated from air.
Pressure swing separation systems are known to offer the best energy efficiency for oxygen separation at small production rates. Systems using the Skarstrom PSA cycle (described in Pressure Swing Adsorption by Douglas M. Ruthven et al., John Wiley & Sons, Inc., 1994, hereinby incorporated by reference, Section 3.2.1) for medical oxygen production are common examples of these small scale systems and are familiar to those skilled in the art. These systems are known to consume about 350 watts of electrical power to produce about 5 liters per minute of oxygen with about 90% purity.
The portable concentrators are battery powered to eliminate tethering utility cords and similar power supply structures attached to the apparatus. Research efforts were directed toward energy efficiency of the separation process. As previously noted, pressure swing separation systems are known to offer the best energy efficiency for oxygen separation at small production rates. Prior art oxygen separators were measured, and the performance and behavior of one of these commonly used systems was analyzed—the currently popular Invacare model IRC5LX (specifications available from www.invacare.com). In this device, an electrically driven pneumatic compressor cycled air from 1 to 3 atmospheres pressure, following the Skarstrom cycle steps, through two columnar containers of adsorbent having high adsorption capacity for nitrogen and other polar molecules. By measuring the pneumatic power of the pumped gas stream including the power associated with the adiabatic heating of the pumped gas and comparing that to the electrical power input to the pump, it was determined that much energy was being lost to pump inefficiency. This finding was set aside, and research was focused on exploring the power consumption aspects of the separation cycle steps.
There is a specific amount of theoretical power associated with pumping a stream of gas through a given pressure difference as is required to operate a pressure swing separation system. For example: (1 Liters/Minute flow rate)×(1 Atmosphere pressure rise)=0.592 watts of power. Adiabatic heating of this gas stream consumes additional power in watts. Reducing the pressure change or the flow rate of the pumped gas stream needed to drive the separation cycle steps would therefore directly reduce the power required to produce a given amount of oxygen. Research and testing was done to determine the minimum pump pressure and flow rates to produce a given oxygen separation rate.